1. Field of the Invention
The present invention relates generally to a method and apparatus for depositing molten metal on a substrate using an arc welder.
2. Description of the Prior Art
Objects of various shapes may be formed by the depositing of layers of material on a substrate. A preform is typically used in this process. A preform is a section of material upon and around which the material is deposited. The preform is machined so as to reflect the final shape of the built-up object. Often, the deposited material will bond to the preform. Thus, the use of a preform typically requires the additional steps in the manufacturing process of machining the preform and removing the preform after fabrication.
Other methods of building objects by material deposition have attempted to eliminate the use of a conventional preform. For example, U.S. Pat. No. 4,775,092 to Edmonds et al. provides a method and apparatus for building objects by welding without the use of a conventional preform. The technique of Edmonds, however, involves running a welding current from the consumable material feed to the just deposited material.
One type of material used in such material deposition processes are metals. A typical means of depositing metals in a manner that allows the deposited metal to be bonded to other metal layers is through welding. However, prior art welding techniques such as is shown in prior art FIG. 1 typically require a substrate made of a conductive material so that a welding current may be directed through the substrate. The arc caused by the welding current then melts feed metal placed adjacent the substrate. These prior art welding techniques can cause the just-deposited metal as well as the previously applied layers of metal and the substrate to be influenced by the welding arc. Such welding arc influences include substantial welding arc penetration into the already-deposited metal which results in the remelting of the already-deposited metal or substrate. When the deposited metal is substantially remelted, there is an accompanying loss in integrity of the shape of the deposited metal. If layers adjacent to the initial layers and substrate have different compositions, remelt could cause the dissimilar materials to mix. Thus, typical welding techniques are inappropriate for the fabrication of objects having accurate dimensions and shapes. Prior art welding methods also cannot weld onto a nonconductive or poorly conductive substrate.